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Does soy protein reduce 'bad' cholesterol? The debate continues

There is an ongoing debate surrounding soy protein and its influence on cholesterol. A new meta-analysis digs into the existing data and concludes that the protein does, indeed, reduce levels of "bad" cholesterol.

Soybeans are among the few vegetable-based foods that contain all of the essential amino acids.

As it stands, the Food and Drug Administration (FDA) includes soy protein in its list of foods that can lower cholesterol.

However, they are considering removing it from this list because studies have provided inconsistent results.

If the FDA do remove it, manufacturers who market products that include soy would no longer be able to label them as heart-healthy. The FDA are basing their potential change in stance on the findings of 46 trials.

Recently, researchers — many from St. Michael's Hospital in Toronto, Canada — decided to revisit the data and run a meta-analysis on the papers in question.

Revisiting the soy debate

Of the 46 studies that the FDA had chosen, 43 provided enough data to be added to the scientists' analysis. In total, 41 studies looked specifically at low-density lipoprotein (LDL) cholesterol, commonly called bad cholesterol.

LDL cholesterol earns its bad name because, when it builds up in arteries, it increases the risk of stroke and heart disease. Any food that can reduce this risk is of great interest.

"Soy protein significantly reduced LDL cholesterol by approximately 3–4% in adults. Our data support the advice given to the general public internationally to increase plant protein intake."

Although the effect size seems small, the results are significant. The authors also believe that, in the real world, the effect may be stronger. They argue that when someone adds soy protein to their diet, in most cases, it will replace other sources of protein that have high levels of LDL cholesterol, such as meat and dairy.

Dr. David Jenkins, who led the study, explains, "When one adds the displacement of high saturated fat and cholesterol-rich meats to a diet that includes soy, the reduction of cholesterol could be greater."

A study published in 2010 examines this displacement. The authors concluded that when combining direct LDL reduction from soy protein with displacement, overall, LDL cholesterol would be reduced by 3.6–6.0%.

Limitations and high hopes

As the authors of the recent investigation explain, a significant limitation of their research is that it only looked at a small subset of relevant studies. However, the purpose of this study was to test the strength of the FDA's conclusions using the very data that they had used to draw their conclusions.

The authors write that "These data were extracted by the FDA as representing those trials on which a final decision would be made concerning the soy protein health claim. Because we are addressing the question raised by the FDA, our inclusion criteria included only those trials selected by the FDA."

It is also worth noting that the studies that the scientists analyzed only used a total of 2,607 participants; of these, only 37% were men. Also, the majority of women that were involved in these trials were postmenopausal. In other words, the demographics of the studies do not match the demographics of the public at large.

However, to reiterate, the main thrust of this study was not to collate all relevant data; it was specifically designed to test the FDA's change in stance.

Other official bodies, including Heart UK, the European Atherosclerosis Society, the National Cholesterol Education Program, and the Canadian Cardiovascular Society include soy protein as a heart-healthy food.

The authors hope that the FDA will consider their meta-analysis when discussing whether to keep soy protein in their heart-healthy category.

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